This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Our research involves studying the structure and function of large catalytic RNAs and RNA-protein complexes using x-ray crystallography. Specifically, we are studying group II introns, which are a class of self-splicing ribozymes that can also function as mobile retroelements. Group II introns undergo a two-step splicing process that leads to their excision from pre-mRNAs and results in the ligation of the adjacent exons. They are also thought to be the ancestors of the spliceosomal introns and non-LTR retroelements, which together comprise ~50% of the human genome. The group II intron and the spliceosome also share a conserved, catalytic core. The spliceosome is a multi-megadalton complex which is responsible for excising nuclear introns in eukaryotes. Through studying group II introns, we can also gain an understanding of these more evolutionarily advanced genetic elements.